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While blindness is often regarded as a disability or weakness in humans, the animal kingdom reveals a wondrous array of creatures that challenge this perception.
For these remarkable beings, the absence of sight does not hinder their ability to navigate and thrive in their unique environments. Instead, they have unlocked extraordinary adaptations, honing their other senses to unparalleled levels and seamlessly adjusting to the conditions that shape their lives.
Why are Some Animals Blind?
Imagine living in a world of complete darkness. Having excellent vision probably wouldn’t serve you as well as something like impeccable hearing. While there are many animals that have great night vision, lots of species that live in caves don’t need good eyesight.
Cave-dwelling creatures, or troglobites, to call them by their scientific name, have other senses that allow them to ‘see’ in the dark, and many have lost their eyes completely. If you were to look at these creatures, you probably wouldn’t recognize them and could be forgiven for thinking that they’re an alien species. But that’s because their behavior and anatomy are so different from the animals we see out in the open. What’s more, many troglobite species are endangered owing to their very limited habitat.
Evolution is largely to blame, and I use the term loosely, for these creatures losing their eyesight. According to Darwin, creatures like the Mexican tetra lost their eyes due to disuse. And I’m not just talking about losing the use of their eyes, I mean they have no eyes at all; just a small bump where the eye used to be.
Modern scientists are sure that blindness is down to natural selection and have been observing the behavior of non-cave-dwelling species within a cave environment. While the blind Mexican tetras, that have inhabited caves for millions of years, don’t make any effort to swim toward the light at the cave opening, immigrant specimens do. Essentially this means that there’s no chance of a seeing fish population remaining in the cave.
It’s thought that these, and other fish and cave-dwelling species ended up here accidentally. Millions of years ago, species would end up in a cave and not be able to get out. Where enough of the same species entered the same environment, new populations were made, and evolution did what it needed to do.
And it’s not just fish that have evolved to lose the use of their eyes, many other species have adapted to their dark worlds this way. The naked mole-rat is a prime example of this, and they have a degenerated optic nerve, meaning their vision is pretty terrible. But then, it doesn’t need to be since these animals spend their entire lives under the ground.
Common Adaptations among Blind Animals
Just because an animal is blind that doesn’t mean that they are not adept at finding their way around the world. In fact, many blind animals have special adaptations that make it easy for them to live their lives as effectively as sighted animals.
Enhanced Sense of Smell & Hearing
One of the most common adaptations in blind animals are heightened senses such as hearing and smell. This is seen in various species of bats and rodents whose amazing other senses allow them to navigate the world as if they could see.
Let’s take bats for example. While they aren’t as blind as myth would have you believe, they don’t rely on their sight as much in the dark as they do on their hearing. They use echolocation by emitting a series of high-pitched sounds that ping off things in the environment, such as prey, and then bounce back to the bat’s super-sensitive ears. This essentially allows them to ‘see’ the world around them without actually using their eyes.
Increased Tactile Sensitivity
Many blind animals have an incredible sense of touch and are easily able to pick up on vibrations which helps them to find their next meal. Take the naked mole-rat, for example, which is able to pick up on tiny environmental changes, leading it to its prey and helping it get around.
There are species of insects that live under the ground whose eyesight is terrible. However, they have very sensitive antennas that they use to feel their way around. These antennas are usually much longer than those of insects that live on the surface. Other insects, and several species of cave-dwelling spiders are able to sense changes in the air movement, including the current and vibrations which tells them if prey is lurking around the corner.
Another fantastic way that blind animals use tactile sensitivity is via specially adapted pits on the head which act as a sensor, picking up on changes in the water pressure when prey is nearby.
Earlier, I talked about how bats use echolocation to find their prey, but there are some animals, most notably cave fish, that have a sensory electromagnetic field around their bodies. They produce this electric field and use it to navigate the world around them.
Lack of Pigmentation
You’ll notice that many of the animals I will discuss in this post are not brightly colored. Albinism isn’t uncommon in the world of blind animals simply because there’s no need for pigmentation when you live in a cave or under the ground.
On the surface, a lack of pigmentation would mean exposing the animal to the harmful UV rays of the sun and this could be potentially fatal. But for troglobites, they need neither protection from the sun nor any sort of camouflage so have lost their color.
Examples of Blind Animals
There are probably many more blind animals on the planet than you ever imagined. But while they cannot see, they have other senses and adaptations that allow them to navigate the world, hunt, and even find a mate!
1. Texas Blind Salamander (Eurycea rathbuni)
The Texas blind salamander is only found in the San Marco area of Texas, so has a very limited range and is therefore listed as endangered. With a colorless body, a wide flat head, and a long tail the animal is perfectly adapted to live in its subterranean environment.
Texas blind salamanders have vestigial eyes which are located under the skin meaning they have totally lost their ability to see. But this doesn’t mean that they aren’t adept hunters because they are able to sense changes in the water pressure by moving their heads from side to side.
You’ll find these salamanders in the Edwards Aquifer, where they hunt for invertebrates, snails, and shrimp. They are equipped with gills on the side of the head which allow them to take oxygen from the still waters.
2. Mexican Tetra (Astyanax mexicanus)
The Mexican tetra is perhaps one of the most talked about blind animals and a species of eyeless fish, sometimes called the blind cave fish. There are two types of Mexican tetras; those that live in caves and those that live on the surface. The troglobite populations have totally lost their eyes with nothing more than cysts where they once were.
However, this does not mean that they aren’t able to catch a meal because they have an amazing sense of smell. What’s more, these small fish are effectively able to pick up on vibrations and changes in the water, which helps them to navigate. It’s also thought that their taste receptors have evolved differently from their surface level cousins.
Another amazing adaptation of these fish is that the cave-dwelling populations seem to have much larger red blood cells. This allows them to release more hemoglobin to transport oxygen around the body more efficiently in an environment where oxygen levels are lower.
Interestingly, Mexican tetras that live in caves sleep for less than two hours a day. While there are several theories as to why this is, a popular one is that sleeping less gives them more opportunities to search for food in an environment where food is scarce.
3. Blind Cave Eel (Ophisternon candidum)
The blind cave eel is a rare species hailing from Australia. It’s a pretty weird-looking creature with light pink skin, no scales, no fins, and no eyes. This is the largest known species of cave-dwelling fish that grows to around 16 inches (41 cm). But despite this, not much is known about it owing to limited populations.
Blind cave eels might not have eyes, but their elongated bodies are perfect for burrowing, which is one of the ways they find food. What’s more, the blood vessels and nerves of the blind cave eel are very close to the surface of the skin. This means that they have a much more responsive sense of touch.
4. Ganges River Dolphin (Platanista gangetica)
These South Asian river dolphins are only found in the Ganges and Indus rivers, and this limited range has resulted in them being listed as endangered.
Living in murky waters means that having good eyesight is of no use when it comes to hunting. However, like other dolphin species, the Ganges river dolphin uses echolocation to search for prey and navigate the water. They emit a series of clicking sounds that bounce back and tell them exactly where objects are.
The dolphin will completely submerge itself, performing echolocation, searching for prey among the rocks such as catfish, prawns, shrimp, and clams.
5. Naked Mole-Rat (Heterocephalus glaber)
One of the most amazing things about the naked mole rat is that it spends its entire life underground. The only time they will come to the surface is in the event their burrow is flooded or otherwise compromised.
Spending all that time under the ground means that functional eyes would be of little use. However, they do have eyes, they’re just very small with a degenerated optic nerve, and the animal often keeps them closed when moving through tunnels.
But they’re still great at moving around under the ground thanks to super sensitive whiskers, which help them to navigate. They don’t need to hunt for food very often as they feed on tubers, and one large tuber may feed a colony for months at a time. What’s more, they’re known to recycle their poop to gain extra nutrients.
An amazing fact about the naked mole rat is that cancer has never been detected in the species. For this reason, they’re often used in research to find cancer treatments for humans.
6. Texas Blind Snake (Leptotyphlops dulcis)
The Texas blind snake is native to arid and desert regions of North America. Although, they do require moisture and logs or rocks within their habitat which is why they’re often found on the edges of desert areas.
While the Texas blind snake does have eyes, they are located under translucent scales, which understandably affects their vision. Moreover, these snakes only have a few teeth and don’t typically grow to more than 12 inches (30 cm).
They’re rarely seen on the surface, being a burrowing species, and only come out at night to look for food. Despite not having good eyesight, they are able to detect changes in the light and use pheromone communication with others of the species.
7. Brahminy Blind Snake (Indotyphlops braminus)
Deep brown to black in color and growing no more than 6 inches (16 cm), the brahminy blind snake is a small species from southern Asia although they’ve been introduced to Florida. They’re often mistaken for the earthworm but upon closer inspection, you’ll notice that they’re not segmented.
Bhaminy blind snakes do have remnants of eyes but unless you look very closely, you wouldn’t see them. While these eyes do not have visual abilities, they are able to detect light which is one of the ways these snakes navigate the world.
All brahminy blind snakes are born female and remain this way through their entire lives. They do not require sex for reproduction.
8. Kaua’i Cave Wolf Spider (Adelocosa anops)
The Kaua’i wolf spider is limited to a very small area on the island of Kaua’i inn Hawaii that covers no more than 4.06 square miles (10.5 square kilometers). They’re one of the rarest spiders in the world, with just six known populations, and nobody has ever seen more than 30 together at a time.
Despite this, these wolf spiders seem to thrive in caves, even though they have no eyes. They do have sighted relatives that live close to the surface, however. While lacking eyes, the spider is still an active hunter that uses its other senses to detect prey. We aren’t entirely sure what it feeds on, but it’s theorized that amphipods make up a large part of its diet.
Known locally as the blind spider, these arachnids are unlike many other cave dwellers in that they have not lost their pigmentation. Adults are usually brown in color with bright orange legs. They’re harmless to humans.
9. Southern Cave Crayfish (Orconectes australis)
The southern cave crayfish was long thought to be extinct until it was rediscovered in a cave in Alabama. There are lots of species of cave crayfish but they’re particularly abundant in Alabama and Florida although numbers are still in decline owing to bat populations and water pollution.
Southern cave crayfish is believed to have an incredibly long lifespan and scientists put this down to their extremely slow metabolism. Just one of the adaptations of cave life. It’s suggested that the longest-living specimens may survive for as many as 176 years!
Lacking pigmentation and having no sight, it’s clear that these animals have evolved to live in darkness. However, they are equipped with long antennae which allow them to feel the world around them.
10. Eastern Mole (Scalopus aquaticus)
The eastern mole, sometimes called the common mole, is native to North America and prefers forested or open habitats with sandy soil. The eyes are completely covered in hair and the mole also has no visible ears, giving it a rather distinct appearance.
While the eyes are covered in fur, as well as a layer of skin, they’re still able to detect light which aids the mole in hunting and navigation. Moreover, there is a touch-sensitive pad located on the nose which further aids the creature as it moves around. Eastern moles have terrible hearing but their sense of touch and smell more than makes up for this.
In fact, their sense of smell is so fine-tuned that eastern moles are able to not only pick up on odors but also sense which direction they are coming from.
11. Bee Creek Cave Harvestman (Texella reddelli)
The Bee Creek Cave Harvestman is a species of endangered arachnid that is endemic to the United States, specifically to central Texas.
Unlike their terrestrial relatives, the harvestmen do not have great vision. They have small eyes, but their vision is limited. However, they compensate for this with long appendages, which provide them with an excellent sense of touch.
The Bee Creek Cave Harvestman is primarily found in caves in central Texas, including those along the Jollyville Plateau.
As for their feeding habits, they primarily feed on invertebrates, but additional specific information about their diet and reproductive habits is limited.
12. Olm (Proteus anguinus)
The olm is a species of salamander found in the Karst caves in Slovenia and Croatia. They’re the largest of all cave salamanders, growing up to 12 inches (30 cm) in length. Sadly, they are now listed as vulnerable on the IUCN Red List.
Olms have eyes but they’re so underdeveloped and sit beneath the skin that they’re as good as useless. But instead of using visual cues to hunt, they are equipped with an excellent sense of smell and hearing. On top of this, olms are able to use chemoreceptors and electroreceptors to catch their prey.
Amazingly, these creatures are able to live for as long as 12 years without food owing to their ability to drastically slow down their metabolism. Moreover, it’s been reported that these creatures can live for as long as 100 years, although the average lifespan is around 68 years.
13. Narrow-Necked Blind Cave Beetle (Leptodirus hochenwartii)
There are around 200 species of cave beetle found in North America, including the narrow-necked cave beetle. These beetles prefer larger caves with high humidity levels and low temperatures and were first described in 1831, making them the first beetle of their kind to be discovered.
Narrow-necked cave beetles do not have working eyes but are instead equipped with long antennae for feeling as well as longer legs which also aid their sense of touch. This enables them to search for the animal droppings and fungi that they feed on.
Like many other species of sightless troglobites, narrow-necked cave beetles lack pigmentation and are unable to fly.
14. Martialis heureka
Martialis heureka is a species of ant that was discovered recently in the year 2000. The name of the ant comes from the meaning ‘from Mars’ owing to its alien-like appearance and while it was only discovered in the last 20 or so years, it’s thought to be the oldest living relative of the very first ants on earth.
A subterranean species, Martialis heureka is blind and this blindness is thought to have evolved over the years, owing to their underground environment. It also lacks pigmentation having lived in darkness for millions of years.
However, they’re still formidable hunters because they have long mandibles that act like forceps and allow them to catch prey. They’re also equipped with long antennae, which they use to feel their way around.
15. Star-Nosed Mole (Condylura cristata)
The star-nosed mole is perhaps one of the oddest-looking creatures on this list. It takes its name from the star-shaped appendages on the face, which make up its nose with a series of appendages called Eimer’s organs.
While the star-nosed mole is essentially blind, these Eimer’s organs allow it to use electroreception to hunt for prey. What’s more, it’s since been discovered that this feature also allows the mole to exploit prey and this has earned it the title of the fastest-eating mammal.
Found in the eastern wetlands of North America, the star-nosed mole’s nose contains more than 30,000 sensory cells. When hunting, they are able to touch their nose to the ground at a rate of 12 touches every second!
16. Yeti Crab (Kiwa hirsuta)
Yeti crabs were only discovered in 2005 and live in the South Pacific Ocean. They get their name from the silky, light-colored, bristle-like hairs that cover the body, giving it the appearance of a yeti.
Like many animals that live in dark environments, the yeti crab lacks pigmentation, and the bristles are thought to be used to detoxify prey before feeding. What’s more, the yeti crab has vastly reduced eyes and is as good as completely blind.
But being blind doesn’t stop these creatures from sustaining themselves. They feed primarily on the bacteria that collect on their bristles, so their meals come directly to them.
Hydra are found in both temperate and tropical waters and are a genus of freshwater organisms that are well known for their immortality. These amazing little creatures are able to regenerate so that they essentially never die!
A relative of the jellyfish, hydra do not have eyes, but scientists believe that they rely on light in order to find their prey, thanks to their special ability to sense light, despite being blind. This is because of opsins called cnidocytes located in their tentacles that not only detect light but can also respond to chemicals and touch.
Hydras have clear tubular bodies with a distinct crown and resemble a dandelion seed! They don’t typically grow any larger than 1 inch (2.5 cm) in length and as well as not having eyes, they also lack a brain and heart!
18. Tumbling Creek Cavesnail (Antrobia culveri)
The tumbling creek cavesnail is in a genus all of its own, Antrobia, and is an endangered species found only in the Tumbling Creek Cave System in Missouri. It’s found on the undersides of rocks where it’s thought that the species feeds on bat dropping runoff.
These cave snails lack pigmentation so much that they almost appear transparent. Not only do they have no eyes, but they also lack mouths.
Sadly, the number of Tumbling Creek cavesnails has declined significantly. There were around 15,000 individuals when they were discovered but things like water pollution has caused them to decrease in number.